The subject invention relates to dynamic motion sensors which can be mounted to a structural member to continuously monitor and record the lateral movement of the structural member. The structural member is typically a load bearing support such as a driven pile or shaft, but the device can also be used directly in soil where an inclinometer casing has been installed.
During the testing phase of building or bridge construction, lateral (horizontal) forces are applied to foundations installed deep into the ground to test structural performance. Currently, measurements of lateral displacements below the ground surface can only be recorded for static load tests. During these static load tests, forces are incrementally and constantly imparted on the foundation. The lateral movement is typically measured by measuring and sensing devices such as strain gages or other displacement mechanisms such as inclinometers. One such example of a strain gage measurement device is disclosed in U.S. Pat. No. 3,500,549 to Smith. The Smith ""549 patent does not teach of using an accelerometer to measure dynamic movement.
A profile of deflected reinforced concrete foundations cannot usually be generated from strain gages. This is primarily due to the changing moment of inertia after tension cracks form in the concrete. Further, inclinometers cannot take measurements at a fast enough rate to record dynamic displacements. Hence, during dynamic tests, e.g. ship impact simulations, only the portion of the foundation above ground can be instrumented and monitored for displacement.
In addition, the prior art, including the Smith ""549 patent, does not include an adjustable orientating device which allows the measuring and sensing device to be inserted into a variety of different sized holes. In other words, the prior art measuring and sensing devices are only designed for a specific size opening.
Accordingly, there is a need for a motion sensor that can be used to continuously measure and record the lateral motion of deep foundations, e.g. driven piles or shafts, during transient dynamic loads. In addition, there is a need for a motion sensor which is versatile enough to conform to a variety of different sized openings or cavities.
A lateral motion sensing assembly for sensing movement experienced by a structural member. The sensing assembly comprises a support body and a measuring device mounted to the support body for measuring movement of the structural member. The assembly is characterized by at least one lever arm pivotally mounted to the support body for removably securing the support body to the structural member. The measuring device is an accelerometer mounted to the support body between the lever arms and aligned with an anticipated line of motion for measuring movement of the structural member along the line of motion.
Accordingly, the subject invention provides for a below ground motion sensor that can be used and reused to continuously measure and record the lateral motion of deep foundations. In addition, the subject invention provides a versatile motion sensor which may be inserted into a variety of different shaped or sized cavities.